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RE: Radiographic inspection

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I have worked in the commercial nuclear industry as well as at DOE
nuclear facilities and this problem has been around for many years in
our industry.  I've seen everything from had-held units to a system
which required two operators.   The latest was a system that used a
color LCD screen indicating depth and size.  The equipment cost about
$25,000, and used the same technology as a system costing a quarter of
this, but without the fancy color monitor.  I have learned that the
operator's experience is the key in the effectiveness.  

What do we do when drilling into a post-tensioned slab?  First, don't!
Second, find another way.  Third, find someone who really knows what
they're doing.  Even when we identify the reinforcing (or tendon, in
this case) we use a ground-fault switch to stop the drill when metal is
contacted.  This has proved very, effective, when drilling around 60ksi
reinforcing steel.  Always us a non-tungsten carbide tipped bit, as this
will stop someone stupid from cutting too far.  

Our construction folk will use pilot holes, but keep this under control,
to locate the reinforcing, which seems effective.  Your radiograph
solution is very costly if used on a wall/slab that is 1-1/2" or more in
thickness.  If you always want to sleep at night, spend the money and
radiograph, it's the sure method.  If you're awake watching the late
show anyway, then save you contractor some money and us an
electromagnetic system or nothing.  A middle of the path approach are
the electromagnetic systems used by a proven operator.  Kinda like
"witching for water" (which I've done to find 72" diameter water pipes.
Once again, the operator wih make or break you.

Good luck

Scott Horn
Bechtel

>-----Original Message-----
>From:	Sam Love [SMTP:loveengr(--nospam--at)email.msn.com]
>Sent:	Saturday, March 28, 1998 2:36 PM
>To:	SEAOC
>Subject:	Radiographic inspection
>
>I am on a committee to answer questions asked in Structure Magazine
>published quarterly by the National Council of Structural Engineers
>Associations.  I am asking for responses to be sent to me at
>loveengr(--nospam--at)msn.com so I can summarize them and come up with a consensus of
>opinion.
>
>1.  Occasionally it is necessary to drill holes through post-tensioned slabs
>for anchor bolts and sometimes 6" diameter holes.  Can holes be drilled
>safely without  breaking a cable?  What happens if a cable is broken?  Are
>there other methods of detecting cables besides radiographic inspection?
>
>Sam Love
>Love Engineering
>Ogden, Utah
>
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